16 Mr Harris on Magnetic Intensity by the 
therefore, might be employed to detect changes in tension, at any 
time and place, provided the force which induced motion in the 
needle, and that force by which it would be eventually reduced 
to rest, without the ring, were both constant quantities. But such 
is not the case. We may, however, reverse the experiment with 
advantage, and cause the ring e¢, Fig. 8, to oscillate about the bar 
m, which may be conveniently fixed within the ring, so as just to 
clear it ; and thus a comparative measure of the force of a bar at 
its poles may be arrived at, by observing the influence of the mag- 
net in reducing the ring to rest. This experiment may be ma- 
naged in the following way. 
2g. A ring of copper ¢, Fig. 8, of about 0,4 of an inch wide, 
and the 1th or the 0,2 of an inch thick, is suspended by two pa- 
rallel threads of silk fibre over a graduated circle, as shewn in the 
figure. The threads are fixed in a diameter of the circle, by means 
of a cross bar of brass a 6, and at about the 1th of an inch dis- 
tance on each side of the centre. The ring is to be accurately 
balanced, and carefully adjusted to parallelism by means of the 
sliding wires at w, from which it is suspended, and its index points, 
1, 2, 3, 4, fixed at each of its quadrants, brought exactly over the 
zeros on the graduated card below. The ring may be suspended 
by means of the brass plane at w, in the frame-work above men- 
tioned, Fig. 3, fixed on the bar f’, and hence be substituted 
occasionally for the magnetic bar. 
29. The ring thus circumstanced, is to be deflected by means 
of the forked lever above mentioned, Fig. 4, from the direc- 
tion of the parallel threads of suspension ; and again set free at 
any given angle by means of the forked portions acting on 
the transverse bar from which the ring is hung. In this case 
a long and steady state of vibration will be obtained, in con- 
sequence of the centre of gravity of the mass constantly 
rising and falling as the ring swings from one extremity of 
the are of vibration to the other. Now, if the number of 
vibrations made by the ring alone, between given points, on the 
